Ramp metering for lane-free traffic of automated vehicles via ramp vehicle speed control

• A new ramp metering method for CAVs driving in a lane-free environment based on variable speed control. • Proposing a zone structure for the on-ramp and two feedback controllers for the proposed ramp metering scheme. • Design of appropriate vehicle movement strategy for lane-free environments with special focus on swift merging behavior. • Extensions of the lane-free microscopic simulator TrafficFluid-Sim for the merge area. • Comparing traffic-light based ramp metering with VSC-based ramp metering by extending the vehicle movement strategy. A new ramp metering method for Connected and Automated Vehicles (CAVs) driving in a lane-free environment is developed and tested at the microscopic operational level. CAVs drive on the mainstream, on the on-ramp and in the merge area according to an ad-hoc movement strategy that takes inspiration from adaptive cruise control, with notable extensions made to accommodate lane-free driving and vehicle nudging. Appropriate settings enable seamless and safe merging from the on-ramp onto the highway. A new approach for ramp metering is proposed to effectively avoid the capacity drop occurring in merge areas due to merge congestion. The approach is based on zone separation of the on-ramp and vehicle speed control in each zone as key components for CAV ramp metering, instead of the conventional traffic signals, to avoid stop-and-go of queueing vehicles, thus mitigating fuel consumption and emissions. In this context, two feedback control strategies are introduced; the first one controlling the ramp flow and subsequently translating this into the desired speed of ramp vehicles; and the second one regulating directly the desired speed of vehicles in the ramp; both in response to the current mainstream density. The results achieved through TrafficFluid-Sim, a microscopic lane-free traffic simulation platform built on SUMO, provide evidence of the feasibility of the proposed ramp metering strategy, ensuring both smooth merging and capacity flow on the mainstream. It is also demonstrated that the introduced vehicle speed control reduces vehicle stops and emissions on the on-ramp, compared to conventional ramp metering with traffic signals.